1. Field of the Invention
The field of the invention relates to telecommunication technologies, and in particular, to the provisioning and delivery of emergency call services in telecommunication networks.
2. Description of the Prior Art
Emergency call services, such as 911, are a vital component of most telecommunication services. The provisioning and delivery of emergency services requires a complex interaction between services providers, such as telecommunication carriers, and public safety elements. One important aspect of providing emergency call services is the ability for an emergency responder to call back a caller in the event of a disconnection. However, recent advances in telecommunication technologies have reduced the ability for emergency responders to call back callers.
In the prior art, most users placed emergency calls over the public switched telephone network (PSTN). In the PSTN, a caller can be identified by the physical line over which the emergency call is placed. Even in a case where the line involved includes a caller identification block, the line remains identifiable by the originating switch. The phone number associated with the line can be passed on to the emergency service responder at the appropriate public safety answering point (PSAP). In the event of a service disconnect, the emergency responder can out dial the phone number to reconnect with the caller.
One new telecommunication technology is Voice over Internet Protocol (VoIP). In the case of VoIP, end users have a wide variety of service options, including the ability to block network elements from passing on their call back number to other network elements. In addition, end users are able to provide call back numbers that, when dialed, do not reach back to the user. Unfortunately, the call back number of a VoIP caller cannot be identified by a phone line, as opposed to in the PSTN. As a result, emergency responders are often times unable to call back VoIP-callers in the event of call disconnects.
FIG. 1 illustrates a communication network 100 in an example of the prior art for providing call back numbers to emergency responders for VoIP callers. Communication network 100 includes VoIP network 110, session initiation protocol (SIP) proxy 105, SIP phone 101, emergency information system (EIS) 115, automatic location identification (ALI) database 116, PSTN 120, and PSAP 125.
In this example, a user using SIP phone 101 places an emergency phone call, such as by dialing 911. Typically, SIP proxy 105 communicates with EIS 115 to determine an appropriate PSAP for the call. EIS 115 selects the PSAP and provides the PSAP information to SIP proxy 105. EIS 115 also determines service information for the call, such as the location of and call back number for SIP phone 101. EIS 115 provides the service information to ALI database 116, along with a key. ALI database stores the service information in association with the key. EIS 115 also provides the key to SIP proxy 105.
SIP proxy 105 then communicates with elements of VoIP network 110, such as a media gateway controller, to setup a call leg from SIP phone 101 to PSTN 120. The media gateway controller communicates with elements of PSTN 120, such as a selective router, to establish a call leg through PSTN 120 to PSAP 125. Included in the call setup process, the key is communicated from SIP proxy 105 to PSAP 125 in the form of an ESRK, ESRN, or ESQK. PSAP 125 queries ALI database 116 with the key to obtain the service information stored by ALI database 116 in association with the key. In this manner, operators at PSAP 120 are able to call back the user in the event of a service disconnection.
FIG. 2 illustrates a flow diagram in an example of the prior art to more clearly describe how a call back number is provided to a PSAP. To begin, SIP phone 101 transmits call signaling, such as a SIP invite message, to SIP proxy 105. The SIP invite message includes several information fields. One of the fields is a from field that indicates the sender of the message. The from field is typically populated with a user identification, such as a SIP user ID. SIP user IDs are often times in the form of userID@network.com. Another field is the called number field. In this case, the called number field indicates 911.
In response to the first invite message, SIP proxy 105 transmits another SIP invite to EIS 115. The second SIP invite also includes the user ID in the from field. EIS 115 performs a database lookup to a database system to determine a call back number based on the user ID. The database system typically contains user IDs stored in association with 10 digit telephone numbers.
Upon determining the call back number, EIS 115 transfers the key and call back number to ALI database 120. ALI database 120 stores the call back number in association with the key. EIS 115 also transfers call signaling to SIP proxy 105 indicating the appropriate PSAP and the key. SIP proxy 105 proceeds to setup the emergency call between SIP phone 101 and PSAP 120. During the call setup process, the key is passed to PSAP 120. PSAP 120 queries ALI database 120 with the key to determine the call back number for the call.
Eventually, call communications commence between an operator at PSAP 120 and the user at SIP phone 101. In the event of an on-hook event or some other service disruption, the operator can call back the user using the provided call back number. Call communications can be re-established and emergency service can continue.
As illustrated in FIG. 2, the prior art contains significant drawbacks in the provisioning and delivery of emergency call services. For example, EIS 115 is required to perform a database look-up based on a user ID in order to determine a call back number for the emergency call, costing valuable time and resources. In addition, storing and maintaining call back numbers at EIS 115 is costly and error prone. Further problematically, users are able to hack into the various fields of SIP invite messages. This reduces the reliability of user IDs provided from SIP phones and further impacts the ability of emergency responders to call back VoIP callers in the event of service disruptions.